Thermal and magnetic trip circuit breaker



A118- 19 l947- M. BINGENHEIMER 2,425,983

AND IAGHETIC TRIP CIRCUIT BRBAKER Filed July 24, 1943` 67 wmaEssEs: 65 INVENTOR a Z Me/r/b/hyenhe/mer. (f f2/y Patented Aug. 19, 1947 THERMAL AND MAGNETIC TRIP CIRCUIT BREAKER Melvin Bingenhcimer, East McKeesport, Pa., as-

signor 'to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 24, 1943, Serial No. 495,979

The invention relates to circuit interrupters and, more particularly, to electroresponsive trip devices for controlling automatic opening operation of a circuit breaker.

An object of the invention is the provision of a circuit breaker with an improved thermal-magnetic current responsive trip device of novel construction whereby it will not be falsely operated by or in response to shocks or vibration.

Another object of the invention is the provision of a circuit breaker with an improved thermal trip device comprising a current responsive bimetallic strip novelly arranged' so that it will give the same deflection as conventional bimetal trip elements of the same dimension and yet which is capable of exerting a very much stronger tripping force than conventional bimetal elements of the samev size.

Another object of the invention is the provision of a circuit breaker with an improved thermalmagnetic trip device comprising a current responsive bimetal element and a cooperating electromagnet for at times actuating the element, the parts being constructed and arranged so that the bimetal element is free to deilect even when the device is actuated magnetically. 'I'his maintains the accuracy of calibration of the bimetal element despite short circuit operations of the device.

Another object of the invention is the provision of a circuit breaker with a very simple thermal magnetic trip device wherein the magnetic means acts to move the bimetal trip element for instantaneous tripping and the parts are so arranged s'claims. (ol. zoo-ss) that the air gap of the magnet is not changed upon heat deflection of the bimetal element.

Another object of the invention in accordance with a modication thereof is the provision of anv improved thermal magnetic circuit breaker trip. device wherein the bimetal element operates independently at times to trip the breaker and also operates jointly with the magnetic means at other times in tripping the breaker.

Another object of the invention is the provision of a circuit breaker with an improved thermal 2 and mode of operation oi the invention together with additional objects and advantages thereof will be best understood from the following detailed description of several embodiments thereof when read in conjunction with the accompanying drawing, in which:

Figure l. is -a vertical sectional view of a circuit breaker embodying a trip device constructed in `accordance with one embodiment of the inven- Fig. 3 is 'a fragmentary sectional view on ak larger scale showing another modication of thel invention; and i Fig. 4 is a section-al view on an enlarged'scale v taken substantially along the line IV-IV of Fig. l.

The present invention is illustrated in the drawing as applied to a circuit breaker mechanism similar to that disclosed in Patent 2,284,825, granted June 2, 1942, to O. S. Jennings and H. S.-

Gano and assigned to the assignee of the present invention. It is to be understood, however, that the improved trip device ci the present invention may be applied to many other types of circuit breaker mechanisms.

Referring to the drawing, the circuit breaker to which the improved trip device is applied coinprises a base 5 and cooperating removable cover 1 both of insulating material, a pair of end terminals 9 and II mounted in recesses in the ends of the base, a stationary contact I3, a cooperating movable contact I5 and an operating mechanism indicated generally at I1, y

The stationary contact I3 is electrically connected to the upper terminal 9, and has associated therewith an arc extinguisher I9 of the slotted metal plate type for extinguishing arcs drawn between the contacts upon interruption of the circuit. The movable contact I5 is carried by a resilient spring contact arm 2| of conducting material secured at its lower end to a channel-shaped member 23 which is pivotally mounted by means of a pivot pin 25 on a yU-shaped metal frame 21. The frame 2l is secured to the base 5 and has spaced side walls between which the channelshaped contact supporting member 23 is disposed.

The operating -mechanism I1 of the circuit breaker comprises a toggle consisting of links 29 and 3| connected to the movable contact. arm, a releasable carrier lever 33 for releasably supporting the outer end of. the toggle, a U-shaped ,ing lever 35.

operating member and a pair of overcenter springs 39 (only one being shown). The toggle link 29 is pivotally connected at 4| to the channel-'shaped contact supporting member 23 and the outer end of this link is pivotally connected to the link 3| by a pivot pin 43. The link 3| is in turn pivotally connected to the releasable supporting lever by a pivot pin 41. pivotally mounted on a pivot pin 49 extending transversely between the sides of the U-shaped frame 21. The .legs of the U-shaped operating lever 35 are pivotally mounted at 36 on the sides of the frame 21, and this operating member has an operating handle 5i of insulating material secured to the outer end thereof. A knob portion of the operating handle projects through an. elongated slot provided therefor in the cover 1. The pair of overcenter springs 39 are disposed on opposite sides of'the lever 33 andlink 3| and are connected. at one euri to the .knee pivot pin d3 of the toggle and at t e otiier end are conm nected to the outer en'l i ...e iiwshaped operat- The Carr lever 't3 is always biased. in a counterclockwise direction by the operating springs 39 but is normally restrained or latched in the position shown in Fig. i. hy a latch of the trip device which will be hereinafter'described..

When the carrier lever thus r strained in latch* ing position, it forms fined support for the outer end of the operating toggle to permit man ual operation of the breaker. When the breaker is in closed position. the contacts are restrained in this position by the carrier lever 33 as long as it is held in latched position, as shown in Fig. i.

To manually open the circuit breaker, the operating handle 5| is moved downwardly to the oi position. This moves the line of action of the springs 39 below the pivot 41, causing the toggle 29-3l to collapse and the switch arm 2l to be moved toppen position with a snap action. To manually close the circuit breaker, the operating handle 5| is moved upwardly to the on" position shown. This movement of the handle moves the line of action of the springs 39 above the pivot 41 whereupon the toggle is actuated to the extended position shown and the switch arm 2| consequently moved to closed position with a snap action.

Automatic opening of the circuit breaker in response to an overload condition occurs when the trip device effects release of the carrier lever 33. When the carrier lever is thus released, it is movedcin a counterclockwise direction by the operating springs 39 causing the toggle 29-3I to collapse and the switch arm 2| to move to open position with a snap action. During this opera tion, the operating handle is moved to an intermediate indicating position by shifting of the position of the operating springs 39. Before the breaker can again be closed, the releasable lever 33 must be reset to latched position to reset the mechanism. This is accomplished by moving the operating handle downwardly as far as vit will go in the Voir direction. A resetting projection 53 on the operating member moves the carrier lever 33 back to its latched position upon reset ting movement of the operating handle to the "olT position.

The trip device includes a flat straight'strip or bar 55 of bimetallic material which may be formed by stamping the same from a stock sheet of bimetallic material. In accordance with the invention, the bimetal element is pivotally mounted intermediate its ends and at its center of gravity on a. supporting bracket 51 or other suitable supporting means.

The lever 33 is 'bimetal The bracket 51 is secured to the base by means of a screw 58 and has a pair of downwardly bent ears or projections 59 formed integral therewith at the outerv end thereof. As a convenient means of pivoting the bimetal clement, it is formed with a pair of projections 6| (Fig. 2) ex tending from the opposite side edges thereof. A pair of cylindrical sleeves or washers 63 preferably, although not necessarily, of insulating material are mounted on the pivot projections 5| of the bimetal element. The sleeves 63 are rotatably engaged in cylindrical bearing openings provided in the spaced depending projections 59 of the bracket 51. The bimetal element is thus mounted for pivotal movement on the supporting projections 55 of the bracket. In making the device the parts are so constructed that the pivot axis of the' bimetal element will be located as closely as possible to the center of gravity of the bimetal element so that this element will as :nearly as possible be statically and dynamically balanced with respect to its pivot. The bimetal element 55 is disposed with its high expansion side nearest the breaker mechanism.. 'When the element is heated a predetermined amount, it will deect in a direction. to release the lever 33 of the circuit breaker mechanism. .dn adjusting screw' B5 extending through a bracket 61 secured to the base 5 is disposed to engage the low expansion side of the bimetal element 55 adjacent the inner end of the element. This inner end. of the bimetal element is maintained against the adjusting screw 65 by means of a helical tension spring 81 disposed between the inner end of the bimetal element and the base. A latch element 69 is carried by the outer free end of the bimetal element 55 for engaging a curved latch piece 1| secured to the lower end of the releasable carrier lever 33 to normally restrain the carrier member in the latched position shown in Fig. 1. The curved latch piece 1| is insulated from the carrier lever so that no current will flow through the carrier lever to the element 55. The latch element 69 is adjustable in order to adjust the amount of latch overlap between it and the latch piece 1| and for this purpose the latch element has-a threaded portion which threads through a washer secured in an opening provided therefor in the outer end of the bimetal element 55. The lower threaded end of the latch element 69 is provided with a screwdriver slot to permit adjustment of the latch element.

The bimetal element 55 is adapted to be heated in response to the current of the circuit through the breaker and for this purpose a portion of the bimetal element is connected in series circuit with the contacts of the breaker. The outer end of the bimetal element is electrically connected by a flexible shunt conductor to the lower terminal Another exible shunt conductor 14 connected at its upper end to the switch arm 2| has its lower end connected to the magnet 1-5 which is connected by exible conductor 83 to the inner end of the bimetal element 55.

When thevbreaker is in the closed position, the current of the circuit flows therethrough from the upper terminal 9, through the contacts |3 and I5, switch arm 2|, flexible shunt conductor 14, magnet 15, flexible conductor 83, through the bimetal element 55, and through the exible shunt conductor 85 to the lower terminal of the circuit breaker. The ow of normal rated current through the breaker does not produce sufiicient heating of the bimetal element tocause s a substantial amount of bending thereof. When an overload occurs in the circuit. however, theA overload current heats the bimetal element and when heated al predetermined amount by the overload current, the bimetal element bends or deiiects to the position indicated by the dotted lines in Fig. l, thereby causing the latch element l to disengage the latch piece 1| and eiiect release of the carrier lever The circuit breaker mechanism is thereupon tripped and the contacts automatically opened in the manner previously described.

In operating to trip the breaker as just dev scribed, when the bimetal element reaches the temperature at which it begins to warp or bend, the inner end of the element presses against the adjusting screw 55 with a force proportional to the latch load. Since the pivot of the bimetal is xed, the bending motion of the portion of the bimetal between its pivot 5I and its inner end is transmitted to the outer half of the bimetal .as

The time required for heating the bimetal element a predetermined amount by the overload currentsintroduces a time delay prior to tripping of the breaker. This time delay varies inversely as the magnitude oi the overload current so that the breaker will be tripped more quickly in response to heavy overload currents than in response to lower overload currents.

By pivotally mounting the bimetal element 55 at its center of gravity, the trip device is made substantially shocky proof, that is, the bimetal element will not be falsely operated to trip/the `breaker inresponse to shocks or vibration. The

mounting arrangement of the bimetal element possesses another important advantage asv explained above, namely that due to the leverage obtained, the bimetal element is capable of exerting a tripping force many times larger than conventional bimetal trip elements oi the samesize which are flxedly mounted at one end.

One feature of the invention is that an electromagnet is provided for moving the bimetal element about its pivot to trip the breaker instantaneously upon the occurrence of heavy overloads or short circuits. The electromagnet 15 is mounted on the bracket 51 adjacent the inner end of the bimetal element 55 on the side thereof opposite the adjusting screw 85. The electromagnet comprises a U-shaped core 11 (Fig. 4) of magnetic material and acoil or energizing winding 19 wound upon one leg of the core. The ends of the legs of the core 11 are disposed in spaced relation to the inner end of the bimetal element 55 so that an air gap is provided between this end of the bimetal element and the two pole faces of the core 11. Since the bimeta1 element is at least partly of magnetic material, the inner end thereof adjacent the core 11 forms the armature of the electromagnet and is adapted to be attracted against the pole faces of the electromagnet when the coil 19 is energized a predetermined amount.

With the connection shown in Fig. l, substantially the whole length of the bimetal element is directly heated by current flow.' It longer time l delay operation of the bimetal is desired, the ccnl ductor 85 may be connected to an intermediate point of the bimetal element so that only a portion of the bimetal element is directly heated by `current now, the remaining portion being heated indirectly by conduction.

The electromagnet 15 is not energized a sumcient amount to move the bimetal element 55 against the force oi' the spring 81 by normal rated current or by overload currents up to a predetermined value. However, when an overload above a predetermined value, for example, an overload current above 8 to l0 times the normal rated current, occurs in the circuit. the electromagnet 15 is sufficiently energized thereby to strongly attract the inner end oi' the bimetal element 55 and move the element about its pivot 6I in a releasing direction, thereby releasing the latch 581l and tripping the circuit breaker. The bimetal element 55 is actuated substantially instantaneously bythe electromagnet so that tripping of the breaker takes place substantially instantaneously upon the occurrence of an overload above the predetermined magnitude.

The electromagnet 15 in this modiilcation of the invention is located adjacent the inner end of the bimetal element 55 substantially directly opposite the stop screw 65, and since this end of the bimetal element is maintained in engagement with the screw during bending or warping of the bimetal element in response to overloads, the air gap of the electromagnet remains substantially constant and is not changed to any substantial degree by such warping or bending oi the bimetal element. Consequently, the instantaneous tripping point provided by the electromagnet 15 remains constant and is not changed by thermal deflection of the bimetal element.

It Will be noted that the bimetal element 55 is free to deflect or bend as far as it wants to when the element is heated in response to overload current, and heat deflection or bending of the element is not obstructed by the electromagnet 15 even when the inner end of the bimetal element has been moved into engagement with4 the poles of the electromagnet during magnetic tripping. Consequently, the calibration and accuracy of thermal operation of the bimetal trip element remains constant and is not changed after tripping of the breaker on heavy overloads Acc or short circuits. This is because the bimetal element is free to bend in response to heating thereof and is not subjected to stresses which might change its calibration.

Another modification of the invention is shown in Fig. 3. This modication is similar in structure to the embodiment shown in Fig. 1 'except that the electromagnet 15' in this instance is mounted adjacent a portion of the bimetal element 55 which deects or materially changes its position when the bimetal element bends or warps when heated by overload current. This results in a cooperative thermal and magnetic trip action wherein tripping of the breaker is at times effected as a result of the joint action of both thermal bending of the bimetal element and the magnetic attraction of the instantaneous tripping electromagnet.

Except for the change in location of the electromagnet, the parts and structure of this modiiication are identical to the embodiment shown in Fig'. l and previously described, and it -is therefore unnecessary to describe the structure again.

Parts identical to those shown in Fig. 1 are identified by the same reference character.

Referring to Fig. 3, the electromagnet T5 is mounted on the bracket 51 in a position such that its pole faces are disposed opposite a portion of the bimetal element substantially midway between the pivot 6I and the inner end of the bimetal element. This portion of the bimetal element opposite the pole faces of the magnet is deflected a substantial amount toward the magnet poles when the bimetal element bends in response to overload currents. Consequently, as the bimetal element starts to bend in response to heating thereof by overload curlrent, the portion thereof opposite the pole faces of the electromagnet i5 move closer to the magnet shortening the air gap therebetween. The reluctance of the magnetic circuit is thus decreased so that the pull of the electromagnet on the biinetal element increases considerably until.

point is reached at which the electromagnet suddenly actuates the birnetal element 55 about its pivot El thereby releasing the latch and tripping the circuit breaker. With this construction, the circuit breaker will be tripped with shorter time delay action on overloads of intermediate value than in the case of the embodiment shown in Fig. l.

The electromagnet in Fig. 3 is also operable to effect instantaneous tripping of the circuit breaker upon the occurrence of an overload current above a predetermined value, for example, above 8 to 1i) times the normal rated current. When an overload above the predetermined magnltude occurs, the'pull of the electromagnet 15' on the blmetal element 55 becomes sufiicient to move the bimetal element 55 about its pivot El thereby releasing the latch and tripping the breaker. The instantaneous magnetic tripping operation takes place independently of any heat deflection of the bimetal element.

In the Fig. 3 modification, the major portion of the bimetal element is freel to deflect when heated without obstruction by the electromagnet, even though the inner portion of the bimetal element has been moved to attracted position against the magnet.

In each of the embodiments of the invention, 4the trip device can be calibrated or adjusted by means of the screw 65 or the adjustable latch 69. In the Fig. 3 embodiment, thermal trip calibration or adjustment may be obtained by means of the adjustable latch 69 and the magnetic or instantaneous tripping point adjusted by means of the screw 65.

It will be understood that a separate armature for the electromagnet may be attached to the bimetal element 55 instead of relying on the magnetic material in the bimetal element itself for the armature.

The element 55 need not be entirely of bimetallic material throughout its entire length. A portion of the length of the element may be of a single metal. If a longer delay is desired, a. part of the element 55 may be constructed of heating resistance 'material and serve as the heater to heat the remaining portion of bimetallic material.

While the invention has been disclosed in accordance with the provisions of 'the patent statutes, it is to be understood that various changes in the structural details and arrangement of parts thereof may be made without departing from some of the essential features of the invention.

lil

,portion. stop means-engaging the low expansion side of said element adjacent one end thereof and permitting pivotal movement oi' said end 'away from the stop means, said bimetal element bending when heated a predetermined amount in response to overload current to cause tripping ot the circuit breaker, and electromagnetic means energized in response to the current of the circuit and acting on said bimetal element on the same side of its pivot as does said stop means for moving said bimetal element about its pivot to instantaneously cause tripping of the breaker upon the occurrence of an overload current above a predetermined magnitude.

In a circuit breaker, a. trip device for tripping the breaker` comprising a bimetal trip element heated in response to the current of the circuit and having a high expansion side and a low expansion side, means pivotally mounting said bimetal element adjacent its mid portion, stop means engaging the low expansion side of said element adjacent one end thereof, said blmetal element bending when heated a predetermined amount in response to overload current to cause trlppingof the circuit breaker, an electromagnet energized in response to the current of the circuit operable to move said bimetal element about its pivot to cause tripping of the breaker upon the occurrence of an overload current in the circuit above a predetermined magnitude, and said electromagnet acting on said bimetal element adjacent said stop means so that the major portion of said blmetal element can bend its maximum amount free of restraint by said electromagnet.

3. In a circuit breaker, a trip device for tripping the breaker comprising a bimetal trip element heated in response to the current of the circuit and having a. high expansion side and a low expansion side, means pivotally mounting said bimetal element intermediate its ends, stop means engaging the low expansion side of said element adjacent one end thereof, spring means acting on said one end to bias it in engagement with said stop means, said bimetal element bending when heated a predetermined amount by overload current to cause tripping of the circuit breaker, an electromagnet energized in response to the current and mounted adjacent said one end of said bimetal element on which said spring acts and on .the high expansion side thereof, said electromagnet being operable to move said bimetal element about its pivot to cause tripping of the circuit breaker upon the occurrence of an overload current above a. predetermined magnitude in the circuit.

4. In a circuit breaker, a, trip device therefor comprising a bimetal trip element heated in response to the current of the circuit and having a high expansion side and a low expansion side, means pivotally mounting said element intermediate its ends, stop means engaging the low expansion side of said element adjacent one end thereof, spring means biasing said one end of said element in engagement with said stop means, said bimetal element bending when heated a predetermined amount in response to overload current to cause tripping of the circuit breaker, and

' an electromagnet energized in response to the vcurrent of the circuit and mounted between said stop means and the pivot and adjacent a portion of the bimetal element that substantially deflects when the bimetal element is heated apredetermined amount by overload current, said electromagnet being operable to move said bimetal element about its pivot to cause tripping of the breaker upon the occurrence of an overload current above a predetermined magnitude.

5. In a. circuit breaker, a trip device therefor comprisinga bimetal trip element heated in response to the'current of the circuit and having a high expansion side and a low expansion side, means pivotally mounting said element intermediate its ends, stop means engaging the low expansion side of said element adjacent one end thereof, spring means biasing said one end of said element in engagement with said stop means, said bimetal element bending when heated a predetermined amount in response to overload current to cause tripping of the circuit breaker, and an electromagnet energized in response to the current of the circuit mounted adjacent said bimetal element on the. high expansion side at a position along the length of the bimetal element intermediate the pivot and the said one end of the bimetal element, said eiectromagnet being operable to move said bimetal element about its pivot to trip the circuit breaker upon the occurrence of an overload in thecircuit above a predetermined magnitude.

-6. In a circuit controlling device, a substan-- tially straight'bimetallic control element having a high expansion side and a low expansion side, means pivotally mounting said element adjacent its mid portion, stop means engaging the low expansion side of said element adjacent one end thereof, spring means biasing said element in engagement with said stop means, said bimetal element bending when heated a predetermined able contacts and operating means therefor inl cluding a, member releasable to cause opening of determined amount in response to overload current to cause said latch to release said releasable member, and an electromagnet energized by the current of the circuit and mounted adjacent said bimetal element at the opposite side oi' the pivot from said latch portion for moving said bimetal element about `its pivot to cause said latch portion to release said member upon the occurrence of? an overload current above a predetermined magnitude.

8. In a circuit controlling device, a bimetallic element responsive thermally to a condition, of the circuit, mounting means for said bimetallic element holding a point adjacent one end and a point intermediate the ends of said element substantially stationary during thermal bending of the bimetallic element to cause deflection of the other end thereof, means for controlling the circuit actuated by said other end of the bimetallic element, and magnetic means acting only on said bimetallic element at a point on the opposite side of said intermediate point from said other end which is thermally deflected for also causing deflection of said other end.

MELvIN BINGENHEIMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,027,238 f Lindstrom Jan. 7, 1936 2,203,462 Frank June 4, 1940 2,325,717 Swingle Aug. 3, 1943 2,214,695 Jennings Sept. 10, 1940 2,067,797 Smith Jan. 12, 1937 2,178,083 i ,Sandln i.-- Oct. 31, 1939 '2,162,577 Gano June 13, 1939 2,376,759 Dyer et a1 May 22, 1945 

